Preheat the oven to 160C/325F and grease and line an 8x8 inch square pan. I spray my pans with cooking spray and then place two strips of grease proof paper into my pan; one across, and one top to bottom. This makes removal later on really easy!
Place butter and sugar into a large bowl, or the bowl of your stand mixer and beat until light and fluffy, around 2 minutes on medium-high speed.
Add in the flour, salt and vanilla, scraping down the sides as necessary, then mix on low speed until the mixture begins to come together. Turn up the mixer to medium speed until you have a soft, smooth dough.
Place 3/4 of the dough into your prepared pan and press into a level layer. I use a measuring cup sprayed with cooking spray to press mine in as it's easy and you get an even layer!
Place in the oven for 12-15 minutes until slightly puffy.
Spread 2/3 of a can of Carnation Caramel into an even layer on top of the caramel.
Crumble the remaining 1/4 of your shortbread mixture over the top of the caramel; it's perfectly fine that it doesn't completely cover the caramel, in fact that's what you want!
Place in the oven for 27-32 minutes until the caramel is bubbling and the shortbread on top is very lightly browned, but looks matte and feels a little firm to the touch.
Leave to cool completely in the pan, before running a knife around the edge of the pan and lifting out. Slice into 9-12 bars and dig in!
Caramel Crumb Bars will keep in an airtight container, at room temperature, for 5 days.